first off let me just say that im new to the whole car scene but i am willing to learn...i have a 92 camaro rs..everything stock..i pulled the 305 and was looking at getting a 350 / L31 4-Bolt Main 350 Short Block Assembly(1-piece rear main seal, 5.700" P/M rods, and nodular iron crankshaft, VR Dish Cast Pistons (-13cc) - Approximatley 9.0 to 1 CR with 64cc heads). now the problem ive run into is...(like i said i have a small amount of knowledge) ive been looking at heads to get and everyone has their own opinion on what is good..but id like to know how i decide on what heads (with their given specs) to get. some one suggested dart 230cc heads and another person said that 230cc is not the right way to go, instead look at 200cc heads. and in one of the posts on this site someone suggested going even lower..maybe something like 170cc or 180cc. someone also suggested getting vortec heads instead of dart's. im just trying to understand how they come to these conclusions...how do i know what specs will help me and what specs will cause me to lose power. and obviously if i ever find the right heads then i'll need a cam...how would i choose a cam based on what heads im gonna get. i guess i can also tell you guys what im looking to achieve out of all this once im done..in the HP department..lets say 400+..budget wise...around $4,000,or slightly more. this wont be an everyday driver nor will it be a drag/strip car either..id like to drive it on the street on nice days and weekends maybe 3 or 4 times a week. im rackin my brain trying to comprehend all this but no one can seem to give me the answer that im lookin for...im grateful that people are trying to help..but just suggesting going with 200cc or 215cc doesnt help, for the simple fact that i dont understand how they came to that conclusion. a more indepth explanation would help me alot...thanks in advance..

your the first person to actually give me a piece of information that helps me a little..thanks...i kinda understand..but let me see if i understand this right..(CID X 0.5 = intake runner volume) so my 350 X 0.5 = 175 irv.. but if i want more HP and torque at lower rpm's then i should look at a 170cc irv..is that right? but then also will the 5.700" p/m rods...is that the right length or would i need longer or shorter rods? or does that not matter that much? let me ask you this...why would someone suggest i get a 230cc head when i could get a 180cc head that has close to the same amount of cfm?

j.d.brown.042964

09-27-2008 02:35 PM

The choice of of runner volume and valvesize should be matched not only to the displacement, but also to intended USEABLE rpm range as well. Everything has to work well together, AS A SYSTEM, to get the best results. As far as 5.7" rodlength, that is what is most popular and "standard" to 350's, although with a change of pistons (having different wristpin location) some builds might use 6.0" rods for reasons specific to that PARTICULAR build. In addition to the WIKI forum, you can gain alot of useable information from searching the knowledge base on this site as well. Many of the factors you need to consider will revolve around what rpm band you will primarily use this engine for. Smaller intake runners will keep lo-rpm velocity and give great torque in the lower rpm range, great throttle response, best overall economy (due to actually UTILIZING most of the fuel mixture being supplied), -but at something of a loss of higher rpm horsepower. Valvesizes figure into this somewhat as well. AS a generic example; a build of a 434 (stroker) smallblock would do very well with 230cc intake runner size and 2.055, or 2.08 intake valves, even at 5500 max rpm,simply due to the larger cubes to fill, whereas to be of any use at all on a 327 you'd have to spin it to 7500 for those sizings to be of benefit, and it would have poor combustion below 3000, (and require a bulletproof bottomend to do so on a continual and ongoing basis). Cam duration and overlap plays into this "usage" equation greatly as well. I would suggest that if you like the shortblock that you are considering, you spend a good deal of time researching what topend components would work well with the existing pistons/cam combo. and choose accordingly. Better to spend alot of time reading now than trying to undo a mismatch later. It appears that's what you are attempting to do now, by asking these questions, and that is well-advised. Try some searches on the knowledgebase and the wiki articles with a few different keywords and/or phrases, and you'll be well-rewarded with very useful stuff. Also check back to this post, as there's some really great knowledge in many of these members years of experience(s). Happy Reading. -Jim.

Nothing's Easy

09-27-2008 09:05 PM

Have a look at the Air Flow Research 180's. They cost a little more but they're pretty much the best you can do for a street/strip 350. Comp Cams recommended a single pattern 08-430-08 or 08-450-8 roller cam to go with the heads since the exhaust port on the heads flow well enough they don't need more exhaust lift or duration.

Nothing's Easy

09-27-2008 09:31 PM

Actually for your intended use of the car a set of vortec heads from Summit would probably be perfect and would cost half as much as anything else. The summit heads will take up to .520" lift. Or a set of GM Performance Parts Vortec heads with some Bee Hive Springs will take up to .550" lift. You should be able to get 400+hp out of them.

HemmiGremmie

09-27-2008 10:14 PM

180-200cc in my .02 for street cars are plenty enuff. 215-230's are gettin a little much in my oppinion. HG

For a good-running 350 street motor, find heads that will flow 220-230 cfm @ 0.400" valve lift on the intake with the smallest runner size. That's what makes the L31 Vortec Chevy heads work so well on a 350. 170cc intake runners and 227 cfm.

The camshaft will be dictated by the static compression ratio of the motor, the desired operating range and the valve lift limit imposed by the valve spring/retainer combination on the heads. If, for instance, you were to build the motor at 9.0:1 with 64 cc heads, you might choose a cam with 0.050" duration figures of between 210 degrees and 225 degrees, depending on lobe separation angle and operating range. It's always best to call your favorite cam grinder and have the tech person spec out a cam for you. The cam should be the LAST component chosen for the motor in most cases. It is possible of course, to build the motor around the cam. But in that case, you have to be flexible in choosing components and building the motor to match the cam so that everything works in harmony.

It's a tragedy, but we see it everyday where some noobie has a 8.5:1 motor and installs a cam that should have been used in a motor with 11.0:1 c.r. Then he shows up on here asking why the motor won't pull the hat off his head.

Although there are numerous compression ratio calculators to be found on the web, here's the way to do it yourself if you want to learn.....

STATIC COMPRESSION RATIO
First, an explanation of what this means. As the piston comes down the bore on the intake stroke, a negative-pressure area is produced in the cylinder. Since nature abhors a vacuum, atmospheric pressure will rush into the cylinder through the intake valve in an attempt to equalize the vacuum to closely match atmospheric pressure. If we introduce fuel into the inrushing air, we have a combustible air/fuel mixture. The inrushing air/fuel mixture fills all available spaces and crevices until the intake valve closes. When the piston reverses direction to ascend up the bore, this mixture is compressed into a smaller volume. It is the total volume of mixture pushed into the cylinder/combustion chamber/piston deck height volume/piston eyebrow or dish volume/head gasket volume compared to the compressed volume of mixture with the piston at top dead center that we are dealing with here.

The ratio involved here is no different than any other ratio. If two million people like white cheese and twenty million people like yellow cheese, then yellow cheese is preferred by a ratio of 10 to 1. (twenty divided by two). If there are 937 rocks in a large container and 90 rocks in a smaller container, then the larger container has more rocks by a ratio of 10.41 to 1. (nine-hundred, thirty seven divided by ninety). By the same token, if 749 cc's of mixture are pushed into the available volume in one cylinder of a motor and the mixture is compressed into an available volume of 86 cc's, then the static compression ratio of the cylinder is 8.70 to 1, expressed as 8.70:1 (seven-hundred, forty nine divided by eighty six). (cubic inches times 16.387 = cubic centimeters).

The volume available to be filled with the intake valve open includes the swept volume of the piston (.7854 X bore in inches X bore in inches X stroke in inches X 16.387 = cylinder cc's), combustion chamber volume (normally given in cc's), piston crown volume with a flat-top or dished piston (normally given in cc's), head gasket volume (.7854 X gasket bore in inches X gasket bore in inches X compressed thickness in inches X 16.387 = gasket cc's) and piston deck height (.7854 X cylinder bore in inches X cylinder bore in inches X distance measured from piston crown to block deck with piston at TDC in inches X 16.387 = piston deck height volume). You must have all 5 of these volumes to correctly determine the static compression ratio of the motor.

The volume available to be compressed into will include 4 of these volumes. You would leave out cylinder volume, because now the piston will be at top dead center and the cylinder volume will be out of play.

Let's build a 383 with Vortec heads so we can plug in some of this knowledge.

A 350 block, bored 0.030" with a 400 stroke crank will be .7854 X 4.030" X 4.030" X 3.750" times 16.387 to equal 783.84 cc's in the cylinder.

Vortec heads have a published volume of 64 cc's.

The piston is down in the bore 0.015" with the piston at top dead center, so the piston deck height will be .7854 X 4.030" X 4.030" X 0.015" X 16.387 to equal 3.13 cc's in the piston deck height.

The pistons are flat-top with 6 cc's of eyebrows in the crown according to information published by the piston manufacturer.

We're using a GM #10105117 head gasket that has a published bore of 4.000" and compressed thickness of 0.028". We chose this gasket thickness, so that when added to the piston deck height, our squish will measure out at 0.043" and should work well with our pump gas motor to prevent detonation. .7854 X 4.000" X 4.000" X 0.028" X 16.387 = 5.76 cc's in the gasket.

Now, we add up all 5 of these values. 783.84 + 64.00 + 3.13 + 6.00 + 5.76 = 862.73 cc's pushed in on the intake stroke with the intake valve open.

Now, we add up 4 of the values, leaving out cylinder volume. 64.00 + 3.13 + 6.00 + 5.76 = 78.89 cc's into which the mixture is compressed.

Now, we divide 862.73 by 78.89 to arrive at a 10.93 static compression ratio.

By breaking all sharp corners in the chamber and on the piston which could glow hot, de-burring the spark plug electrodes and last plug thread in the heads, optimizing the ignition advance curve and choosing a cam with the proper intake valve closing event (36-42 degrees ABDC @ 0.050" tappet lift), this motor should run on premium pump gas without detonating.

weaz4200

09-28-2008 12:22 AM

and thats why im askin, techinspector1...so i dont make a mistake..and so i learn all i need to know in the process..

Quote:

find heads that will flow 220-230 cfm @ 0.400" valve lift on the intake with the smallest runner size

The AFR 180's are, in my opinion, the finest heads you can bolt onto a 355 Chevy to make power in a street-friendly rpm range. This AFR page has the flow chart at the bottom.....http://www.airflowresearch.com/180sbc_sh.php

I forgot to mention the Comp Cams guy recommended to install the 08-450-08 cam 4 degrees advanced (its just an advance keyway on most after market timing chains). Its supposed to give the cam a better bottom end for cars without the recommended gears or 2500 stall converter.

Now that you've gotten a great start on choosing components for your engine that will work well together to make it a powerful mill, don' forget to set aside some $$$ to upgrade the transmission, suspension, cooling system, and rearend as well. :sweat:

Quote:

i have a 92 camaro rs..everything stock..

That way you won't scatter parts all over the street the first time you hammer it.:smash: Enjoy your build.-Jim :thumbup:

weaz4200

09-28-2008 01:09 PM

so are you guys saying that the AFR 180cc SBC Eliminator Street Heads and the magnum 286HR i suggested in my last post are a good choice? as for the transmission im goin to buy another 700r4 cause i cracked the case when i was pulling the engine..and plus a mechanic told me that my trans was flaring in 1st and 2nd anyways...but i was thinking about ordering the 700r4 and having them change up the stock convertor to something different..but i dont know which one....the suspension..well i dont really know what i should look at getting..what do you guys suggest...the same goes for the cooling system....and the rearend..with that when i called up compcams with a setup i was thinking of getting before...a tech suggested...i change the stall convertor to like a 2000 and change the rearend gears to 3.73... so i might take the stock 2.73 gears and change them to 3.73..id like to hear what you guys think..